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**ABSTRACT:**

Frost\, A. E. 2021. In th e Air Gap of Linear Generators for Wave Power. Digital Comprehensive Sum maries of Uppsala Dissertations from the Faculty of Science and Technolo gy 2084. 96 pp. Uppsala: Uppsala University. ISBN 978-91-513-1322-1.

Wave power conversion is one type of renewable electricity generation . Within wave power\, there are many different concepts\, whereof some u tilizes linear generators for converting the energy in the ocean waves i nto electricity. A linear generator consists of a translator\, which is moving and have magnets of alternating polarity\, and a stator\, which h ave conductors surrounded by laminated steel. Between the translator and stator is an air gap\, which is only a few millimeters wide. All linear generators for wave power\, to the author&rsquo\;s knowledge\, are perm anent-magnet synchronous generators. This thesis looks into the forces a nd power ﬂow in the air gap of linear generators for wave power\, with t he purpose of improving their future performance. The studies have focus ed on permanent magnet synchronous generators for wave power\, but sever al of the results should also be applicable for other applications of li near electrical machines.

Depending on the design of the linear ge nerators\, the translator can move so long that it only partially overla p the stator. This is common among several different wave power concepts with linear generators. When the stator is only partially overlapped by the stator it is denoted as partial stator overlap. It is studied how p artial stator overlap affects the generated electricity\, the absorbed e nergy\, and the tangential and normal force in the air gap. The generate d electricity and absorbed energy of a linear generator are quadraticall y dependent on the partial stator-translator overlap is shown through Fa raday&rsquo\;s law and simulations. Experimental data showed that the ab sorbed energy is both linearly and quadratic depending on partial stator overlap\, where the linear dependence is at least partially due to fric tional losses. Simulated results conﬁrm that voltage is linearly depende nt on partial stator overlap\, which means quadratic dependence between generated electric and partial stator overlap. The simulated forces show ed a linear dependence.

Decades ago\, the Poynting vector was used to derive an expression for the power ﬂow in the air gap of rotating el ectrical machines. In this thesis the equivalent expressions for both ﬂa t and tubular linear electrical machines were derived. The analytical re sults were also compared with results from simulations. Both the analyti cal expressions and simulations showed that tubular and ﬂat linear elect rical machines have slightly different behavior.

**Keywords:
** Linear generator\, Wave Power\, Poynting'\;s theorem\, Part
ial stator overlap\, Permanent-magnet synchronous generator (PMSG)\, Lin
ear electrical machines